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2008 chevy
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3 Posts
Discussion Starter #1 (Edited)
I've read several posts detailing SOME of the issues I'm having, but haven't seen any with ALL of the issues...

I replaced my battery a few weeks back. Almost immediately afterwards the following problems started... let me also preface this with it runs and drives fine. A tech 2 scan tool showed no communication with basically any system except for the motor.

1. Front AC blower started acting funny. At first it would blow at full blast no matter the fan speed setting, then it would blow very gently, again regardless of the fan speed setting. It then abruptly stopped working altogether... aside from one time where it was magically on when I started the truck, and then would not turn off when i shut the vehicle off. I had to disconnect the battery to get it to turn off. The rear seat HVAC works fine. no issues there.

2. Both driver and passenger airbag lights have come on.

The stabilitrack light comes on intermittently, but has done that since I bought this thing 5-6 years ago. Cruise control does not work, again, since I bought it.

3. The low beam headlights come on and off, which is very inconvenient, particularly at night. Hi beams work fine. I've had this particular issue in the past... replaced the HDM relay, and the headlight switch which resolved the issue, but I'm not so sure that they are the problem this time.



I've seen some posts saying a faulty Ignition switch can cause many of these issues. My mechanic (best friend) wants to try a new BCM first... He thinks it's abusrd that the ignition switch can be causing these issues, but I've brought some of the threads I've seen to his attention. Any and all help, insights, advice would be greatly appreciated before I start dumping money into parts.


2008 Trailblazer LT3
4.2 Liter VORTEC in-line 6
Odometer: 172,540
 

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2004 gmc envoy_slt
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2,468 Posts
Yes, ignition switches have cause weird electrical problems. But not like you have.

The front HVAC blower is controlled by the Blower Motor Control module. They have been known to fail in the manner you describe, a power transistor is usually cause.

Air bag faults need to be scanned by a high-end scanner for codes.

The Stabilitrack system relies on the wheel speed sensors among other things. There may be a front wheel speed sensor that is marginal. Cruise control will not function if a speed sensor is bad.

The low beam failure is usually caused by a defective HDM relay, but if replacing that relay does not fix the problem, there may be a problem in the underhood fuse box.
 

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2008 chevy
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3 Posts
Discussion Starter #3 (Edited)
Would a BCM not cause these issues? My mechanic seems to think that’s at least the place to start. All of the issues listed started at the same time after the battery was replaced... He scanned it with a high end snap on scan tool, and it wasn’t able to communicate with several modules, including airbags

As far as the headlights... I’ve had that issue before and replaced the HDM relay, which did the trick. Just swapped it again, and voila headlights are good.

That leaves me with the airbag light on, and AC not blowing... I tried a new ignition switch, as this was the cheapest option, and no dice. I guess my next step will be the blower resistor.
 

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2006 chevy trailblazer_ls
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19 Posts
Find and check all the grounds. Make sure all are clean and tight Don't replace any control mod until you've checked all the grounds.

If you can get a wiring diagram look to see what ground or power they share then check the powers and grounds on the BCM make sure everything is good before you replace the BCM
 

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2009 chevy tb
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28 Posts
Is it safe to assume the battery installation went without incident??...as in, the terminals didnt' short circuit to each other, or ground out, etc?

Considering this problem started with a battery change, I would cut into the battery terminals and look for corrosion or decay. NOTHING will ground properly without a solid battery connection, which includes the cables. Copper wire which is black or green is scrap metal.

Be sure everything, including the ignition key, is OFF before disconnecting the battery. It could be a strange coincidence, but more likely there is something in common...like voltage...that is causing all of these problems. Hopefully nothing is fried.
 
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